Papers by Author: Jesualdo Luiz Rossi

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Authors: Edilson Rosa Barbarosa Jesus, Jesualdo Luiz Rossi
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Authors: M.M. Serna, Edilson Rosa Barbarosa Jesus, E. Galego, Luís Gallego Martinez, H.P.S. Corrêa, Jesualdo Luiz Rossi
Abstract: The aim of the work was to prepare an overview about the microstructures present in high-speed steel, focused on the crystallography of the carbides. High-speed steels are currently obtained by casting, powder metallurgy and more recently spray forming. High-speed steels have a high hardness resulting from a microstructure, which consists of a steel matrix (martensite and ferrite), in which embedded carbides of different crystal structure, chemical composition, morphology and size, exist. These carbides are commonly named MxC, where M represents one or more metallic atoms. These carbides can be identified by X-ray diffraction considering M as a unique metallic atom. In this work, it is discussed, in basis of the first principles of physics crystallography, the validation of this identification when it is considered that other atoms in the structure are substitutional. Further, it is discussed some requirements for data acquisition that allows the Rietveld refinement to be applied on carbide crystallography and phase amount determination.
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Authors: E.A. Martins, Isolda Costa, Jesualdo Luiz Rossi, Hercílio G. De Melo
Abstract: Permanent magnets based on intermetallic compounds are employed in dentistry to fix dental prosthesis. However, these materials are very sensitive to corrosion. In this study the corrosion behavior of a sintered commercial Nd-Fe-B magnet has been investigated at neutral pH in a phosphate buffered solution (PBS). With this aim demagnetized specimens were immersed in the test solution and their corrosion behavior were monitored at increasing test times by means of electrochemical impedance spectroscopy ( EIS ), potentiodynamic polarization curves and surface observation by scanning electron microscopy ( SEM ). Experimental results indicated that the corrosion resistance is seriously affected in this solution. Moreover, no decrease in the intensity of the corrosive attack was verified during test periods of up 4 hours. Impedance results have indicated the occurrence of diffusion controlled phenomenon, likely linked to the presence of pores in the magnet microstructure.
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Authors: Cristiano Stefano Mucsi, Rubens Nunes de Faria, E. Galego, Jesualdo Luiz Rossi
Abstract: The main objective of this work is to present the preliminary results on the analysis of the signals arising from the electrical arc, during the vacuum arc remelting of Zircaloy electrodes, aiming the automation of the fusion process. Zircaloy electrodes were made from compacted chips resultant of the machining of Zircaloy rods. The melts were performed in a prototype (vacuum arc remelting) VAR furnace under low pressure of argon and the arc was fed by a constant DC power source. Both filtered and unfiltered signals were recorded by means of a data acquisition system. The fast Fourier transforms FFT and autocorrelation integral were used as tools for data analysis. The result showed that the events occurring within the electric arc have a strong influence on the electric signals. The analysis allowed inferring that the VAR electric arc system has mainly a chaotic behaviour and sporadic periods of linear behaviour. The conclusion of this work is that a control system may be developed, based on the modelling of the non-linear behaviour of the arc, mainly chaotic. This may allow the achievement of an automatic control for the process and yield better quality products.
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Authors: S.M. Traldi, Isolda Costa, Jesualdo Luiz Rossi
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Authors: L.C. Aranha, Cristiano Stefano Mucsi, F.C. Ceoni, M.C. Alencar, Jesualdo Luiz Rossi
Abstract: This paper presents the initial developments of a prototype device intended to perform measurements of the fastening torque in the range bellow 1 N.m – hereby denominated microtorque. The device is intended to yield data for analysis of in vitro torquing and detorquing experiments, for fixation and removing of abutments in dental implants and implants in artificial bones. The analysis of the data acquired allowed the authors to observe characteristic fingerprints or signal signatures associated to the type of abutment or implant under experimentation as well as of the mechanical prototype characteristics. In this paper, two different systems of abutment and implant were analyzed. The correlation between the phenomena associated to the signal fingerprints indicate that the developed measurement protocol may be extended to other implant / abutment systems. The authors suggest that the insertion and removal torque curves evaluated in this study would facilitated the correlation between the abutments stability in actual patients and the dynamical behavior under masticatory function.
520
Authors: C.P. Couto, R. Politano, Maurilio Pereira Gomes, M.A. Colosio, Jesualdo Luiz Rossi
Abstract: The hot stamping process consists to heat the steel blank, at total austenitization temperatures and to transfer it into the press tooling for forming and fast cooling to fully martensitic transformation. This transference from furnace to press stage promotes some steel oxidation. The application of metallic coatings avoids this phenomenon. The Al-Si coating, a patented process, has been the most applied on steel. Hence, alternative coatings like Zn-Ni are under development. It is known that this furnace heating causes chemical elements diffusion that results in intermetallics formation. This study had the objective of analyze the diffusion profiles of chemical elements present in the substrate, 22MnB5 steel, and coatings of Al-Si and Zn-Ni, using glow-discharge optical emission spectroscopy - GDOES and to correlate the results with those obtained with energy dispersive X-ray spectroscopy - EDS. The results showed that for the Zn-Ni sample, the Zn and Fe profiles at the interfacial zone, are predominant; which justify the high proportion of ZnFe phases as showed using scanning electron microscopy - SEM images. For the Al-Si sample at the interfacial zone, the profile of Al and Fe varies simultaneously; besides that, silicon diffusion in the substrate is more effectively than the nickel diffusion. For this reason, it was possible to identify AlFeSi phase near to the steel substrate.
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Authors: R.M. Lima, Edilson Rosa Barbarosa Jesus, Jesualdo Luiz Rossi
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Authors: Edilson Rosa Barbarosa Jesus, E.S. Jesus Filho, Jesualdo Luiz Rossi
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Authors: E.S. Jesus Filho, Edilson Rosa Barbarosa Jesus, A.H.P. Andrade, Jesualdo Luiz Rossi
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